There are various types of samples in the field of analytical chemistry, and particularly in the medical field, body fluids such as blood, urine, spinal fluid, saliva and the like, are important objects for analysis. There are needs for analyzing such samples in large amount and collectively.
In order to meet such needs, a device for analyzing a sample having a reagent film previously impregnated with a reagent, which is stuck on a strip, has been developed and practically used. In such a device, the reagent film is supplied with a sample such as blood, where a component in the sample is reacted with the reagent to generate a pigment, whereby a color is developed in the reagent film, and the color is analyzed by using an optical measuring apparatus such as a densitometer. By using such a device, operations for preparing a reagent and reacting the reagent with a component in the sample can be simplified, thereby the whole process for analyzing a sample becomes a routine exercise.
In such a device, examples of methods for supplying the reagent film with a sample include, methods utilizing capillarity, spotting, dipping, and the like. Among these methods, methods utilizing capillarity have been most commonly used. Because it is required to intercept external light during optical measuring, it is necessary that a sample supplying portion and an analytical section should be positioned away from each other when the device is set in an optical measuring apparatus. Accordingly, a sample is required to be transferred in the device, therefore capillarity is utilized as a means for transferring the sample. Examples of devices utilizing capillarity are those disclosed in Japanese Patent Application Laid-open No. Hei 4-188065 or in Japanese Patent Application Laid-open No. Sho 57-132900.
FIG. 22 shows a device for analyzing a sample utilizing capillarity. As shown in the drawing, the device comprises a triangular shaped sampling point 42 protruding from an approximately center portion of the front face 44 of a transparent base member 47 made of acrylic resin, a groove 46 extending from the sampling point 42 toward the back portion of the base member 47, and a slot 45 formed as an extension of the groove. Furthermore, a reagent film 48 is stuck on the upper face of the base member 47 on the side of the front face 44, so that it may cover over the groove 46. The structure of the reagent film 48 is determined as appropriate depending upon the type of a sample. For example, when analyzing plasma components of blood, a reagent film having a laminated structure comprising a filtration layer, a reagent layer, a transparent protective layer, and an opaque protective layer, which are laminated in this order from the bottom, in which an observation window 50 is formed for entering light in an approximately center portion of the opaque protective layer, is used.
A sample may be analyzed by using such a device as in the following steps. First, a drop of blood is obtained from a subject and brought into contact with the sampling point 42. Then, the blood is introduced into the groove 46 by capillarity and the whole groove is filled with the blood. When the blood permeates into the reagent film 48 covering over the upper portion of the groove 46, erythrocytes are first removed by the filtration layer, and plasma components reach the reagent layer, where a pigment is generated through a reaction between a reagent in the reagent layer and a component in the plasma, whereby a color is developed in the reagent layer. In this state, the device is set in an optical measuring apparatus such as a densitometer, where the color developed in the reagent layer may be measured by irradiating light from the observation window 50.
However, there are problems as described below in using a device utilizing capillarity.
First, because a capillary channel is required to be continuously filled with a sample in order to cause capillarity, an amount of a sample more than required for analysis is needed. In addition, it takes some time to introduce a sample by capillarity, so that measuring cannot be performed quickly. Furthermore, in body fluids such as blood, there are differences among individuals in properties such as viscosity, which affect capillarity, therefore the time period required for introducing a sample into the analytical part or the like cannot be fixed. As a result, it is difficult to fix a time period required for analysis, such as time for reaction with a reagent. Accordingly, there is a possibility that an error might be caused in analysis results. Furthermore, since the drawing force by capillarity is very weak, it is easily affected by gravitational force. Therefore, when introducing a sample, the gradient of the device should be restricted, and the structure of an optical measuring apparatus should also be limited. Furthermore, the sample supplying portion and the analytical section cannot be positioned apart from each other because of the weakness of the drawing force of capillarity, so that possibilities of contamination during an introduction of a sample or influence of external light cannot be completely eliminated in an optical measuring apparatus.
On the other hand, the spotting method has a disadvantage in that when using blood as the sample, the sampling spot is limited to a fingertip, and sampling from an ear or the abdomen is difficult.